Electrostatic chucks are used in the vacuum chambers of semiconductor processing systems and, in particular plasma processing systems, to secure substrates, such as semiconductor wafers, in a stationary position during a processing step. An electrostatic chuck incorporates one or more electrodes embedded within a dielectric body. A chucking voltage is applied to the electrodes that, by operation of Coulomb's law, establishes a clamping force that attracts the substrate to the surface of the electrostatic chuck. Certain electrostatic chucks provide an attractive clamping force arising from operation of the Johnsen-Rahbek effect. The performance of the electrostatic chuck slowly deteriorates over time such that the clamping force is no longer adequate when the clamping voltage is applied or such that the substrate is not promptly released or dechucked after the chucking voltage is removed.
Significant difficulties arise when an electrostatic chuck having unknown characteristics is initially installed as a replacement for an originally-installed electrostatic chuck in a semiconductor processing system performing a process step or steps in a production line. Specifically, the performance of the replacement chuck may differ from the performance of the originally installed chuck. The replacement chuck should provide substantially the same chucking performance when a chucking voltage is applied and substantially the same dechucking performance when the chucking voltage is removed in comparison with the originally installed chuck in its unused initial state. Moreover, the replacement electrostatic chuck should provide a similar process uniformity as the chuck that it replaced. It is known that processing uniformity varies across the surface of the substrate if the chuck electrode does not deliver the RF power with spatial uniformity to the support surface. The properties of the chuck electrode can vary due to differences introduced during the manufacturing process of various electrodes. If the replacement electrostatic chuck has an inferior performance that is undetected before installation, the chuck is a likely candidate to fail prematurely under normal operating conditions.
Because of the inherent unpredictability in performance, a technician must calibrate the replacement electrostatic chuck after it is installed in the semiconductor processing system and before it is initially used to secure substrates for processing. The calibration procedure idles the processing system for a time sufficient to optimize the performance of the electrostatic chuck. Unless the operational parameters are optimized before initial use, the replacement chuck may not adequately chuck a substrate or, after a chucking voltage is applied and the substrate processed, the replacement chuck may slowly dechuck substrates. If the performance of the electrostatic chuck is known before the chuck is installed in the process chamber, the calibration procedure is significantly simplified and expedited.
Antecedent knowledge of the chuck performance may provide information that can predict the lifetime of the chuck while in service. An electrostatic chuck that exhibits poor initial performance may later prematurely fail and damage either the processing system or the wafer being processed. A failed chuck must be replaced or repaired, which requires idling the processing system. Shutdowns are costly as the downtime has a ripple effect along the production line that significantly decreases the productivity of the production line and increases maintenance costs.
Limited performance testing of the replacement electrostatic chuck may be performed ex-situ on a benchtop before installing the chuck in a semiconductor processing system in a production line. However, the benchtop environment cannot accurately simulate the environment that the chuck would experience within the vacuum chamber and does not expose the chuck to a realistic environment during testing. Because of the significant differences between a benchtop environment and the environment inside an evacuated semiconductor processing system, ex-situ measurements of chuck performance may not accurately predict the performance in the process chamber and under processing conditions. Additional variables, such as exposing the electrostatic chuck to a plasma during testing or heating the chuck to an operating temperature in a vacuum environment, can influence the chuck performance and may provide additional insights into the chuck performance.
With growing requirements for improved diagnostic information regarding the performance of an electrostatic chuck, an objective of this invention is to provide methods to predict the performance of an electrostatic chuck, before the chuck is installed in the vacuum chamber of a semiconductor processing system in a production line, and to use the predicted performance to select chucks having a suitable level of performance.